The large consumer demand for products contained in metal containers creates a correspondingly large demand for metal containers. There are numerous known methods for manufacturing metal containers. These methods produce cans that may be labeled or otherwise decorated in a fashion that is designed to attract consumer attention and convey information.
Cans of the type involved in this application are generally fabricated from three pieces or two pieces. A three piece can comprises a bottom, a top, and a sidewall that are fitted together with at least one joint being welded to form a generally closed, cylindrical unit. The cost of the welding process and the fact that the weldment posed at least a possible contamination problem created a desire for a two-piece can construction.
The two-piece design comprises one drawn piece that comprises the bottom and the sidewall and a second piece that comprises the top. Containers formed by both of these methods normally create straight side walls or, in other words, a cylindrical configuration or, in some cases a conical configuration. Furthermore, the cost of the material used to manufacture the cans has moved the industry to form the cans with increasingly thin material. As the thickness of the material decreases, the ease with which it tears or wrinkles increases. Thus, the machines and methods used to work with this material must take into account that the material will easily wrinkle or tear.
Recently, can purchasers have expressed the desire to purchase a can that has a contoured sidewall. For the purposes of this application, a contoured sidewall is one that has a profile that is not straight. The profile may have a single curve or a plurality of curves. It is believed that cans having a contoured sidewall will be useful for marketing purposes. It is also believed that a can having a contoured sidewall will be attractive to consumers who will identify the contoured can with a specific product. For example, it may be desirable to form a can in the well-known shape of a Coca-Cola beverage bottle. Such a can would enable a consumer to identify the can by its shape as well as by its labeling. An example of such a container may be seen in Kornick Design U.S. Pat. No. 365,501. Another use for a contoured sidewall is to provide portions of the can to assist gripping. These functions are also useful on containers other than metal containers used for beverages. Containers that store food items and other consumer goods will also benefit from having a contoured sidewall.
Known manufacturing methods are not able to economically mass produce containers having a contoured sidewall. One suggested method has been to form a can in a well known manner including the step of ironing the can to initially form the sidewall. An inflatable bladder is then inserted into the can and expanded with compressed air or other fluid substance. The bladder presses outwardly on the sidewall from the inside of the can creating a contoured sidewall. The problem with this process is that the sidewall hardens after it has been ironed. When the bladder is expanded to stretch the hardened wall, the wall tends to split, wrinkle, or crack resulting in rejection of that can. There is, therefore, clearly a need in the art for a method for forming a can having a contoured sidewall utilizing, so far as possible known two piece can forming methods.